Field of the Disclosure
The present subject matter relates to radio frequency identification (“RFID”) devices. More particularly, the present subject matter relates to systems and methods for testing continuously moving RFID straps.
Description of Related Art
RFID tags and labels (collectively referred to herein as “devices”) are widely used to associate an object with an identification code. RFID devices generally have a combination of antennae and analog and/or digital electronics, which may include, for example, communications electronics, data memory, and control logic. For example, RFID tags are used in conjunction with security locks in cars, for access control to buildings, and for tracking inventory and parcels. Some examples of RFID tags and labels appear in U.S. Pat. Nos. 6,107,920; 6,206,292; and 6,262,692, all of which are hereby incorporated herein by reference in their entireties.
One difficulty associated with RFID devices is the need to test operation of such devices as part of the manufacturing or fabrication process. In fabrication of RFID devices, the devices may be formed on a sheet or roll or web of material, closely spaced apart. In traditional methods of activating, reading, and/or detecting RFID devices, an antenna is used to send radio frequency (“RF”) fields over a relatively long range, that is over intervening free space. When such methods are applied to testing closely spaced RFID devices, it is difficult to test a single RFID device, since the RF field interacts with several devices simultaneously, and the various RFID devices may interact with one another.
According to another known approach for testing RFID devices, which is illustrated in FIGS. 1A and 1B, RFID straps S (each of which includes an RFID chip R in contact with and spanning the space between a pair of enlarged contact or terminal pads P) on a web W are tested by contact. In particular, a test system T includes a central controller C which controls the function of the other components of the test system T, which may include a strap detector D, a test head H, a strap marker or chip crusher M, and a conveyor mechanism V for moving the web W with respect to these other components. When an RFID strap S moves (in a left-to-right direction in the orientation of FIGS. 1A and 1B) into place beneath the test head H, a pair of contact pins or probes N of the test head H move downwardly to contact the two contact pads P of the RFID strap S at contact points B (FIG. 1B). The contact pins H measure one or more parameters of the RFID strap S, such as the assembled chip resistance, assembled chip capacitance or RFID read/write functionality, with an RFID strap S being marked as defective or destroyed by the strap marker or chip crusher M if it does not meet preselected performance standards. In this context ‘assembled’ includes additional resistance and/or capacitive components in addition to the chip resistance/capacitance, frequently described as parasitic. The RFID strap S must be stationary when it is being tested, which requires the test system T to include a trigger mechanism that instructs the conveyor V to stop the web W when an RFID strap S is in place.
If multiple RFID straps S are to be tested simultaneously, then during each test cycle, the web W must be moved so as to advance that number of RFID straps S into alignment with the matching number of test heads H. The movement of the web W is then stopped, the contact pins N of the test heads H are brought into engagement with the RFID straps S, and then the process is repeated for the next set of RFID straps S. This further increases the complexity required of the test system T, because a plurality of RFID straps S must be simultaneously aligned with a plurality of test heads H, the multiple test heads H must be precisely moved simultaneously, and the results of multiple test heads H must be precisely matched, all of which requires precise alignment or individual compensation values in the software of the controller C.